Semiconductor device and method of designing the same

ABSTRACT

A semiconductor device includes a first wiring layer, a second wiring layer and an insulating layer provided between the first wiring layer and the second wiring layer. A capacitor has a first electrode formed on the first wiring layer and a second electrode formed on the second wiring layer in such a manner that the second electrode overlaps with the first electrode. To the first electrode, two connection wirings are connected and, to the second electrode, two connection wirings are connected. The two connection wirings are connected to each other with low DC impedance substantially only through the first electrode. Similarly, the two connection wirings are connected to each other with low DC impedance substantially only through the second electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation Application of U.S. patentapplication Ser. No. 12/202,672, filed on Sep. 2, 2008, the entirecontents of which are incorporated herein by reference. The Ser. No.12/202,672 application claimed the benefit of the date of the earlierfiled Japanese Patent Application No. 2007-225199 filed Aug. 31, 2007,the benefit of which is also claimed herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and, inparticular, relates to a technique for detecting a defect of acapacitor.

2. Description of the Related Art

A semiconductor device is constructed by forming circuit elements suchas a transistor, resistor or capacitor on a semiconductor substrate madeof silicon or gallium arsenide and connecting the respective circuitelements through wirings. To easily inspect such semiconductor devices,it is general to use a DC (direct current) test, in which DC voltage andelectric current is applied to a predetermined point of an integratedcircuit formed on a semiconductor device and resulting electricalcharacteristics is measured to subsequently check go or no-go and tomeasure circuit characteristics.

Here is a case where a capacitor is formed on a semiconductor integratedcircuit. The capacitor is essentially open (impedance is infinite) to aDC signal component. Accordingly, in performing a DC test, it wouldappear that the capacitor does not exist against the DC signalcomponent. Accordingly, the DC test has a problem that an unexpectedopen state (that is, high-frequency open failure) due to a disconnectionor manufacturing defect of a capacitor or wiring connected to thecapacitor is difficult to detect.

SUMMARY OF THE INVENTION

In view of the foregoing problem, it is a general purpose of the presentinvention to provide a technique for facilitating detection of an openstate due to manufacturing defect of a capacitor.

An embodiment of the present invention is related to a semiconductordevice having a first wiring layer, a second wiring layer, and aninsulating layer provided between the first wiring layer and the secondwiring layer. The semiconductor device includes a capacitor having afirst electrode formed on the first wiring layer and a second electrodeformed on the second wiring layer in such a manner that the secondelectrode overlaps with the first electrode. Two connection wirings arerespectively connected to the first electrode and the second electrode.

According to this embodiment, if any failure such as a disconnectionoccurs in an electrode of a capacitor or two connection wiringsconnected thereto, DC impedance of a path including the electrode andthe two connection wirings becomes higher than that in a case where nofailure occurs. Hence, any failure in the capacitor can be detected by aDC test, based on a change in DC impedance.

The two connection wirings connected to the first electrode may beconnected to each other with low DC impedance substantially only throughthe first electrode, while the two connection wirings connected to thesecond electrode may be connected to each other with low DC impedancesubstantially only through the second electrode.

With such configuration, in a case where no failure occurs, theimpedance between two nodes to which the two connection wirings arerespectively connected becomes substantially zero. In case where somefailure occurs, on the other hand, the two nodes are in galvanicallyopen state, thus attaining easier failure detection by a DC test.

The first electrode and the second electrode may be rectangular and thetwo connection wirings connected to the first electrode may be led outfrom a common side of the first electrode in a first directionperpendicular to the common side. Accordingly, the two connectionwirings connected to the second electrode may be led out from a commonside of the second electrode in a second direction perpendicular to thecommon side. Here, the rectangular shape includes a square shape.

The first direction and the second direction may be opposite to eachother. And the first direction and the second direction may beperpendicular to each other.

The first wiring layer is the uppermost wiring layer, and the secondwiring layer is a wiring layer lower than the first wiring layer. Thecapacitor may further have a via hole disposed along one side of thesecond electrode and a third electrode connected to the second electrodethrough the via hole and formed on the first wiring layer. The twoconnection wirings connected to the second electrode may be formed onthe first wiring layer and led from the third electrode.

With such configuration, if a disconnection or contact failure occurseven in the third electrode or via hole, such failure can be detected bya DC test.

Another embodiment also relates to a semiconductor device having a firstwiring layer, a second wiring layer and an insulating layer formedbetween the first wiring layer and the second wiring layer. Thesemiconductor device has a capacitor having a first electrode formed onthe first wiring layer and a second electrode formed on the secondwiring layer in such a manner that the second electrode overlaps withthe first electrode. When the capacitor is provided between a firstwiring for connecting between a first node and a second node in anintegrated circuit and a second wiring for connecting between a thirdnode and a fourth node in an integrated circuit, the first electrode ofthe capacitor functions as a part of the first wiring and the secondelectrode of the capacitor functions as a part of the second wiring.

According to the embodiment, if any failure occurs in the capacitor, DC(direct current) impedance between the first node and the second nodebecomes higher or DC impedance between the third node and the fourthnode becomes higher, and thus, such failure can be detected by a DCtest.

The first node and the second node may be connected to each other withlow DC impedance substantially only through the first electrode, whilethe third node and the fourth node may be connected to each other withlow DC impedance substantially only through the second electrode.

With this configuration, if any failure occurs in the capacitor, an openstate is made between the first node and the second node or between thethird node and the fourth node, thus such failure can be detected moreeasily.

Still another embodiment of the present invention is a semiconductordevice. The semiconductor device is constructed by disposing a unit cell(a basic cell). The unit cell is a unit capacitor including a firstelectrode formed on a first wiring layer, a second electrode formed onthe second wiring layer arranged to sandwich an insulating layer withthe first wiring layer in such manner that the second electrode overlapswith the first electrode, two connection wirings connected to the firstelectrode and two connection wires connected to the second electrode.

According to this embodiment, if a disconnection failure occurs in twoconnection wirings connected to an electrode of a capacitor or in theelectrode, DC impedance of a path including the two connection wiringsand the electrode becomes higher than that in a case where no failureoccurs. Hence, any failure in the capacitor can be detected by a DC testbased on a change in DC impedance.

All capacitors formed on the semiconductor device may be constructedwith a unit capacitor as a unit cell. By constructing all capacitorswith such unit cell, failure in all capacitors can be detected.

Still another embodiment of the present invention is a method ofdesigning a semiconductor device. The method includes: registering aunit capacitor, which has a first electrode formed on a first wiringlayer; a second electrode formed on a second wiring layer arranged tosandwich an insulting layer with the first wiring layer, in such amanner that the second electrode overlaps with the first electrode; twoconnection wirings connected to the first electrode; and two connectionwirings connected to the second electrode; reading out a unit cell fromthe library and disposing the unit cell on an integrated circuit, when acapacitor is positioned between a first wiring for connecting between afirst node and a second node in the integrated circuit and a secondwiring for connecting between a third node and a fourth node; andconnecting the first node and the second node to the two connectionwirings connected to the first electrode, respectively and connectingthe third node and the fourth node with the two connection wiringsconnected to the second electrode, respectively.

It is to be noted that any arbitrary combination or rearrangement of theabove-described structural components and so forth is effective as andencompassed by the present embodiments.

Moreover, this summary of the invention does not necessarily describeall necessary features so that the invention may also be asub-combination of these described features.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures, in which:

FIGS. 1A to 1C are views illustrating a configuration of a semiconductordevice having a capacitor according to an embodiment;

FIGS. 2A and 2B are views illustrating connection modes of a capacitorin FIGS. 1A and 1B;

FIGS. 3A to 3D are circuit diagrams and mask layouts illustratingpreferable connection modes of a capacitor; and

FIGS. 4A and 4B are mask layout views illustrating a modified example ofa capacitor in FIG. 1A.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described based on preferredembodiments which do not intend to limit the scope of the presentinvention but exemplify the invention. All of the features and thecombinations thereof described in the embodiment are not necessarilyessential to the invention.

A state where “a member A is connected to a member B” used hereinincludes a case where a member A and a member B are physically anddirectly connected to each other as well as a case where a member A anda member B are indirectly connected to each other through another memberhaving no essential influence on the electrical state. Similarly, astate where “a member C is provided between a member A and a member B”includes a case where a member A and a member C or a member B and themember C are directly connected to each other as well as a case wherethey are indirectly connected through another member having no essentialinfluence on the electrical state.

FIGS. 1A to 1C are views illustrating a configuration of a semiconductordevice 100 having a capacitor 2 according to an embodiment. FIG. 1A is atop view illustrating the semiconductor substrate and FIG. 1B is asectional view taken along line b-b′ in FIG. 1A. FIG. 10 is a circuitsymbol of a capacitor 2 in FIGS. 1A and 1B herein.

As illustrated in FIG. 1B, a semiconductor device 100 includes asubstrate 4, a first wiring layer L1, a second wiring layer L2 and aninsulating layer L3. A semiconductor integrated circuit is constructedof circuit elements using those layers such as transistor, resistor,capacitor, and wires to connect thereof.

The substrate 4 is a semiconductor substrate made of silicon, silicongermanium, gallium arsenide, or the like, or an insulating substratesuch as a glass substrate. The first wiring layer L1 is an uppermostwiring layer. As an upper layer of the first wiring layer L1, apassivation film (not illustrated) is formed. The second wiring layer L2is a wiring layer lower than the first wiring layer L1. The insulatinglayer L3 is provided between the first wiring layer L1 and the secondwiring layer L2. Between the second wiring layer L2 and the capacitor 2,a transistor (not illustrated) or the like is formed. In the presentembodiment, only two wiring layers are illustrated for simpledescription and easy understanding, but in practice, more wiring layersand insulating layers may be formed. On the first wiring layer L1 andthe second wiring layer L2, a wiring for connecting between circuitelements is formed. For such wiring aluminum wiring or copper wiring canbe used for example. Such a configuration of the semiconductor device100 is general and therefore detailed description will not be provided.

The capacitor 2 has a first electrode 10 and a second electrode 12. Thefirst electrode 10 is formed on the first wiring layer L1. The secondelectrode 12 is formed on the second wiring layer L2 in such a mannerthat the second electrode 12 overlaps with the first electrode 10. Asillustrated in FIG. 1A, two connection leading wirings (herein afterreferred to as connection wiring(s)) 16 a, 16 b are connected to thefirst electrode 10. Similarly, from the second electrode 12, twoconnection wirings 18 a, 18 b are connected.

The capacitor 2 further includes a via hole 20 and a third electrode 14.The via hole 20 is disposed along one side of the second electrode 12.The third electrode 14 is formed on the first wiring layer L1 and isconnected with the second electrode 12 through the via hole 20. The twoconnection wirings 18 a, 18 b connected to the second electrode 12 areformed on the first wiring layer L1 and are led out from the thirdelectrode 14. Regarding a circuit symbol in FIG. 10, an electrode on theside where the third electrode 14 is provided is illustrated with adouble line to distinguish the side from the first electrode 10 side.

The first electrode 10 and the second electrode 12 are rectangular. Thetwo connection wirings 16 a, 16 b connected to the first electrode 10are led out from one common side (the left side in FIG. 1A) of the firstelectrode 10 in a first direction perpendicular to the one side(opposite direction to X-axis). The two connection wirings 18 a, 18 bconnected to the second electrode 12 may be led out from one common side(the right side in FIG. 1A) of the second electrode 12 in a seconddirection perpendicular to the one side (X-axis direction). In FIG. 1A,the first direction and the second direction are opposite to each other.

A configuration of the semiconductor device 100 having the capacitor 2is as described above. Next, description will be made on a connectionmode of the capacitor 2 using connection wirings 16 a, 16 b, 18 a, 18 b.FIGS. 2A and 2B are views illustrating connection modes of the capacitor2 in FIGS. 1A to 1C. Here is a case where a capacitor C1 is providedbetween a first wiring W1 connecting between a first node N1 and asecond node N2 in an integrated circuit, and a second wiring W2connecting between a third node N3 and a fourth node N4 in an integratedcircuit as illustrated in FIG. 2A.

When the capacitor 2 in FIG. 1A is used as the capacitor C1, in apreferable embodiment, the capacitor 2 is connected as shown in FIG. 2Bso that the first electrode 10 of the capacitor 2 functions as a part ofthe first wiring W1 and the second electrode 12 functions as a part ofthe second wiring W2.

Looking at a connection mode in FIG. 2B from another point of view, thetwo connection wirings 16 a, 16 b connected to the first electrode 10are connected to each other with low DC impedance substantially onlythrough the first electrode 10. The two connection wirings 18 a, 18 bconnected to the second electrode 12 through the third electrode 14 areconnected with low DC impedance substantially only through the secondelectrode 12. “Low DC impedance” means that a path including the firstelectrode 10 is the only wiring directly connecting the first node N1and the second node N2, or a path including the second electrode 12 isthe only wiring directly connecting the third node N3 and the fourthnode N4. Other than wirings, a circuit element such as a resistor ortransistor, which has significant impedance, may be provided between thefirst node N1 and the second node N2 or between the third node N3 andthe fourth node N4.

By using the capacitor 2 in FIGS. 1A to 1C, if failure such as adisconnection occurs in the first electrode 10 of the capacitor 2 or thetwo connection wirings 16 a, 16 b connected thereto, DC impedances ofthe path (W1) including the two connection wirings 16 a, 16 b and thefirst electrode 10 increase. Accordingly, some influence occurs on agalvanic operation of a circuit including the capacitor 2, and thus, thefailure can be detected. If any failure occurs in the second electrode12 or the two connection wirings 18 a, 18 b connected thereto, thefailure can be detected similarly.

Especially, if the capacitor 2 is connected as illustrated in FIG. 2B sothat the first electrode 10 of the capacitor 2 functions as a part ofthe first wiring W1 and the second electrode 12 of the capacitor 2functions as a part of the second wiring W2, the first wiring W1 or thesecond wiring W2 is cut off when the capacitor 2 has some failure andtherefore the circuit stops to operate. Hence, failure of the capacitor2 can be detected more easily and reliably.

Using a more specific circuit as an example, a preferable connectionmode will be described below. FIGS. 3A to 3D are circuit diagrams andmask layouts illustrating preferable connection modes of a capacitor.

FIGS. 3A and 3B are an equivalent circuit diagram and a mask layoutaccording to the present embodiment, respectively and FIGS. 3C and 3Dare an equivalent circuit diagram and a mask layout using a conventionalcapacitor, respectively. FIGS. 3A to 3D illustrate a case where acapacitor C1 is provided between base and collector of an NPN bipolartransistor Q1.

At first, description will be made on a connection mode using aconventional capacitor C2 referring to FIGS. 3C and 3D. As illustratedin FIG. 3C two electrodes of the conventional capacitor C2 arerespectively connected to one connection wiring. One electrode of thecapacitor C2 is connected with the base of a transistor Q1, while theother electrode of the capacitor C2 is connected with the collector ofthe transistor Q1. As illustrated in FIG. 3D, the capacitor C2 has afirst electrode 10, a second electrode 12 and a third electrode 14. Thefirst electrode 10 and the second electrode 12 are respectivelyconnected to connection wirings 6, 8. One connection wiring 6 isconnected with the base electrode of the transistor Q1. The otherconnection wiring 8 is connected with the collector electrode of thetransistor Q1.

On the other hand, in FIG. 3A, the capacitor 2 described in FIGS. 1A to1C is used as a capacitor C1 provided between the base and collector ofthe transistor Q1. In an equivalent circuit of FIG. 3C, the first nodeN1 corresponds to an input terminal IN and the second node N2corresponds to the base of the transistor Q1. The third node N3corresponds to an output terminal OUT and the fourth node N4 correspondsto the collector of the transistor Q1. In addition, a wiring forconnecting the first node N1 with the second node N2 corresponds to thefirst wiring W1 and a wiring for connecting the third node'N3 with thefourth node N4 corresponds to the second wiring W2. The capacitor C1 isprovided in between the first wiring W1 and the second wiring W2.

Accordingly, when the capacitor 2 according to the present embodiment isused, the connection wiring 16 a is connected to the first node N1 andthe connection wiring 16 b is connected to the second node N2, asillustrated in FIG. 3A, which means that the first electrode 10 of thecapacitor 2 is used as a part of the first wiring W1 for connecting thefirst node N1 with the second node N2. The connection wiring 18 a isconnected to the third node N3 and the connection wiring 18 b isconnected to the fourth node N4, which means that the second electrode12 of the capacitor 2 is used as apart of the second wiring W2 forconnecting the third node N3 with the fourth node N4. FIG. 3B is a masklayout view corresponding to FIG. 3A.

In FIG. 1A, a case where a direction of the connection wirings 16 a, 16b and a direction of the connection wirings 18 a, 18 b are opposite toeach other has been described. It should be noted that a first directionin which the connection wirings 16 a, 16 b are led out and a seconddirection in which the connection wirings 18 a, 18 b are led out areperpendicular to each other in the mask layout view of FIG. 3B. Whichmeans that orientations of the connection wiring 16 and the connectionwiring 18 may be determined considering a positional relationship toother circuit elements and wiring efficiency.

The effect of the semiconductor device according to the presentinvention will be apparent from comparison of FIG. 3A with FIG. 3C. Whena conventional capacitor is used, it has been difficult to detectfailure in the capacitor because the failure has no effect upon a testresult as long as the DC test is used even if failure such as adisconnection or a break occurs in the first electrode 10, the secondelectrode 12 of the capacitor, or the connection wirings 6, 8. On thecontrary, when the capacitor 2 according to the present embodiment isused and connected as illustrated in FIG. 3A, the base or the collectorof the transistor Q1 becomes open and the transistor does not functionwhen some failure occurs in the capacitor 2, thus abnormality or failurein the capacitor can be detected by a DC test.

As described above, with the capacitor 2 according to the presentembodiment, failure in a capacitor may be detected only by a DC testwithout a need of the AC test, which is disadvantageous in cost and testtime.

FIGS. 4A and 4B are a mask layout views illustrating modified example ofa capacitor in FIG. 1A. In a capacitor 2 a in FIG. 4A, the thirdelectrode 14 is not provided, the connection wiring 18 a is connected tothe second electrode 12 through a via hole 20 a, and the connectionwiring 18 b is connected to the second electrode 12 through a via hole20 b. In the capacitor 2 b of FIG. 4B, the connection wirings 18 a, 18 bare provided on the second wiring layer L2 and connected directly to thesecond electrode 12 not through the via hole 20.

Also with the capacitor 2 a or the capacitor 2 b, failure in thecapacitor can be detected by a DC test.

In designing a semiconductor integrated circuit, a concept of a unitcell (basic cell) is used. The unit cell refers to the smallest designunit in a circuit element. By connecting a plurality of unit cells,desired circuit constants, such as resistance, capacitance and emitterarea, can be obtained.

In an embodiment, at least one of the capacitors 2, 2 a, 2 b is used asa unit cell and any capacitor in an integrated circuit is constructedusing such unit cells. Preferably, all capacitors formed on thesemiconductor device are constructed using the unit cells. Byconstructing all capacitors using unit cells, failure in any capacitorcan be detected by a DC test.

To use the capacitors 2, 2 a, 2 b according to the present embodiment asunit cells, it is preferable that the semiconductor device is designedwith the following steps.

1. The capacitors 2, 2 a, 2 b and the like are registered in a libraryof the mask design tool as unit cells.

2. When a capacitor is positioned between the first wiring W1 forconnecting between the first node N1 and the second node N2 in theintegrated circuit and the second wiring W2 for connecting between thethird node N3 and the fourth node N4 in the integrated circuit, a unitcell is read out from the library and positioned on the integratedcircuit.3. The first node N1 and the second node N2 are respectively connectedto the two connection wirings 16 a, 16 b connected to the firstelectrode 10, and the third node N3 and the fourth node N4 arerespectively connected to the two connection wirings 18 a, 18 bconnected to the second electrode 12.

The connection wirings 16 a, 16 b, 18 a, 18 b may be excluded from unitcells. Thus, the unit cells include the first electrode 10 and thesecond electrode 12 and if needed further include the third electrode 14and the via hole 20.

In this case, it is preferable that the semiconductor device is designedaccording to the following steps.

1. The capacitors 2, 2 a, 2 b and the like are registered in a libraryof the mask design tool as unit cells.

2. When a capacitor is positioned between the first wiring W1 forconnecting the first node N1 with the second node N2 in the integratedcircuit and the second wiring W2 for connecting the third node N3 withthe fourth node N4 in the integrated circuit, a unit cell is read outfrom the library and positioned on the integrated circuit.3. The first node N1 is connected with any point of the first electrode10 and the second node N2 is connected with any different point of thefirst electrode 10. Similarly, the third node N3 is connected with anypoint of the second electrode 12 (or the third electrode 14) and thefourth node N4 is connected with any different point of the secondelectrode 12 (or the third electrode 14).

In the semiconductor device designed according to the design method, afailure in a capacitor can be detected easily by a DC test.

The steps 2 and 3 in the two design methods may be performed manually bya designer, however, it is preferable to prepare such process as afunction or a module of an automatic layout tool. Such automatic layouttool reads out net list of a circuit and determines a connectionrelationship between respective elements. The automatic layout tool usesa capacitor registered in the library as a capacitor and dispose at anappropriate position on a substrate. The automatic layout tool furtherconnects two leading wirings provided for each capacitor electrode withother circuit elements according to the procedure of step 3.

In the semiconductor device designed according to the design method, afailure in capacitors can be detected by a DC test.

It is understood by those skilled in the art that the foregoingembodiment is simply illustrative and various changes and variations maybe made in a combination of respective components or respectiveprocesses, and that such changes and variations are within the scope ofthe present invention.

The present embodiments have described a case where two connectionwirings led out from a capacitor electrode are connected with a commonside of the electrode but the present invention is not limited thereto.Which means that the two connection wirings may be respectivelyconnected to different sides.

While the preferred embodiments of the present invention have beendescribed using specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the appendedclaims.

1. A semiconductor device having a first wiring layer, a second wiringlayer and an insulating layer provided between the first wiring layerand the second wiring layer, comprising a capacitor having a firstelectrode formed on the first wiring layer and a second electrode formedon the second wiring layer in such a manner that the second electrodeoverlaps with the first electrode, wherein two connection wirings arerespectively connected to the first electrode and the second electrode,wherein the first electrode and the second electrode are rectangular andthe two connection wirings connected to the first electrode are led outfrom different sides of the first electrode, and the two connectionwirings connected to the second electrode are led out from differentsides of the second electrode.
 2. The semiconductor device according toclaim 1, wherein the two connection wirings connected to the firstelectrode are connected to each other with low DC impedancesubstantially only through the first electrode, and the two connectionwirings connected to the second electrode are connected to each otherwith low DC impedance substantially only through the second electrode.3. The semiconductor device according to claim 1, wherein the firstwiring layer is the uppermost wiring layer, and the second wiring layeris a wiring layer lower than the first wiring layer, the capacitorfurther includes: a via hole disposed along one side of the secondelectrode and a third electrode connected to the second electrodethrough the via hole and formed on the first wiring layer, and the twoconnection wirings connected to the second electrode are formed on thefirst wiring layer and led out from the third electrode.
 4. Asemiconductor device constructed by disposing a unit cell with the unitcell being a unit capacitor including: a first electrode formed on afirst wiring layer; a second electrode formed on a second wiring layerarranged to sandwich an insulating layer with the first wiring layer insuch a manner that the second electrode overlaps with the firstelectrode; two connection wirings connected to the first electrode; andtwo connection wirings connected to the second electrode, wherein thefirst electrode and the second electrode are rectangular and the twoconnection wirings connected to the first electrode are led out fromdifferent sides of the first electrode, and the two connection wiringsconnected to the second electrode are led out from different sides ofthe second electrode.
 5. The semiconductor device according to claim 4,wherein all the capacitors formed thereon are constructed with a unitcapacitor as a unit cell.